As is well-known to boiler operators, sulfur containing fuels, whether it be coal or oil, do present problems not only from a pollutional point of view, i.e., acid smut, but also cause problems with respect to the useful life of metallic equipment and parts which are in contact with the flue gases containing the sulfur biproducts of combustion.
Upon combustion, the sulfur in the fuel is converted to sulfur dioxide and sulfur trioxide. When sulfur trioxide reaches its dew temperature, it reacts with the moisture in the flue gas to produce the very corrosive sulfuric acid. The gases themselves are troublesome as air pollutants, while the acid formed is damaging from corrosion aspects.
As can be appreciated, the greater the sulfur content of the fuel, the more the effects are disastrous. This is particularly the case in industrial and utility operations where low grade oils are used for combustion purposes.
Although many additives have been utilized for the purpose of conditioning flue gases, few additives have found overall success. The reason for the relatively little success in this area of application is felt to be the peculiarities found in the different combustion systems and boiler designs. The gas dynamics and the loads produced, sometimes make chemical treatments for the most part impractical, therefore, requiring a combination of mechanical and chemical treatment.
It was to this problem that the present inventor addressed himself, i.e., the problem of reducing acid smut and acid corrosion of metal parts utilizing a minimum of mechanical and chemical treatment.
The basic area to which the present invention is directed is often referred to in the industry as the "cold-end" of a boiler operation. This area is generalized as being the path in the boiler system that the combustion gases follow after the gases have, in fact, performed their service of heating water, producing steam and/or superheating steam.
In the larger boiler systems, the last stages through which the hot combustion gases flow include the economizer, the air heater, the collection equipment or the electrostatic precipitator, and then the stack through which the gas is discharged.